76 LIBBIE H. HYMAN 



jected and the wealth of experimental data with which it has 

 been presented. Other explanations of amoeboid movement 

 have been so lacking in this respect that I shall not undertake to 

 discuss them, with the exception of the contractility idea of 

 Dellinger which will be referred to in the proper place. 



The surface tension theory, as everyone knows, explains pseudo- 

 podium formation as the result of local diminutions of the tension 

 of the surface of the protoplasm. This idea seems to have origin- 

 ated with Berthold ('86) who based it on certain well-known facts 

 (due chiefly to the experiments of Quincke) concerning the 

 spreading of fluids. Berthold's reasoning is as follows: if the sum 

 of the surface tension between the amoeba and the water, and the 

 amoeba and its substratum is less than the surface tension be- 

 tween the water and the substratum, then the amoeba will 

 necessarily spread between the water and its substratum, owing 

 to the tendency of any such system to bring its surface forces to 

 a minimum value. In other words, anything that lowers the 

 tension of the surfaces of contact of the amoeba will cause it to 

 spread, and these spreadings will be local, i.e., pseudopodia, be- 

 cause of the impossibility of maintaining identical conditions on 

 all sides of the animal. Berthold also explained the production 

 of pseudopodia extending freely into the water on the assump- 

 tions that the tension between the amoeba and the water be re- 

 duced to zero, and that local differences exist in the water. 

 Berthold, however, recognized clearly that alterations in the 

 environment do not adequately explain amoeboid behavior but 

 that chemical differences within the amoeba and modifications 

 resulting from stimulation must be of great importance. 



This conception of Berthold's has been adopted by Rhumbler 

 and has received extensive development in his hands ('98 and 

 subsequent papers). Having made a careful study of the be- 

 havior of amoeboid organisms, Rhumbler attempted to imitate 

 these activities with non-living materials, with such success that 

 he concluded that both sets of phenomena are explicable by 

 means of the same physical laws, the laws that govern the be- 

 havior of fluids, especially those concerning surface tension. 

 Since, Rhumbler argued, inequalities in the surface tension will 



